The present invention relates to a method and a device for presetting the flatness of a rolled strip by presetting the roll nip profile of a roll stand for rolling a rolled strip, with the roll nip profile being influenced by output values for the roll nip profile and the tensile stress distribution being set over the roll nip profile, with the output values for the roll nip profile being determined by using a roll nip profile model which calculates the roll nip profile.
To prevent unevenness in rolling, in particular in cold rolling, influences that would interfere with the required roll nip profile must be counteracted by appropriate setting of the flatness control elements. Until the flatness control used for this purpose has reached a steady state, a lower-quality rolled product known as deviation is produced.
To minimize this deviation and to make the rolling operation more reliable, the object of the present invention is to adjust the mill train so that the rolled strip will have the proper flatness from the beginning. To do so, a presetting function is required. This should determine the cumulative crown, i.e., the roll nip profile, as accurately as possible in advance at the start of a roll pass, i.e., when the strip to be rolled is entering the roll stand, and it should adjust the flatness control elements accordingly.
This object is achieved according to the present invention by providing a method and a device for presetting the roll nip profile of a roll stand for rolling a rolled strip, where the roll nip profile is influenced by output values for the roll nip profile. The tensile stress distribution over the roll nip profile is influenced. The output values for the roll nip profile are determined by using a roll nip profile model which calculates the roll nip profile, with the calculated roll nip profile or an equivalent quantity being linked to a correction value to form a corrected calculated roll nip profile. The roll nip profile model is adapted to the actual roll nip profile of the roll stand by using a correction value. It has been found that especially accurate presetting of the roll nip profile is achieved by using this method.
In an example embodiment of the present invention, the corrected calculated roll nip profile and the actual roll nip profile are compared, a new updated correction value being determined on the basis of this comparison, in particular by weighting with a learning function.
In another example embodiment of the present invention, the actual roll nip profile is determined from values, in particular measured values, for the tensile stress distribution. This determination of the actual roll nip profile from the tensile stress distribution is an especially suitable method of determining the roll nip profile.
In a particularly example embodiment of the present invention, the roll nip profile is first set when the rolled strip enters the stand according to the output values for the roll nip profile calculated by using the roll nip profile model. The roll nip profile is then set according to output values for the roll nip profile calculated by a flatness control. The flatness control assumes the function of setting the output values after measured values for the tensile stress distribution are available and after the flatness control has reached a steady state. Although the roll nip profile is set by the flatness control, the correction factor for the roll nip profile model is calculated anew. The same measured values are used for the tensile stress distribution as for the flatness control. In this way, the roll nip profile model can be corrected without any additional measured values. Another advantage is that many measured values are available for correction of the roll nip profile model, so that an especially good correction of the roll nip profile model is achieved.